The extensive commerical use of push-in type connectors started with the development by Benander of the invention of the U.S. Pat. Nos. 2,705,785 and 2,705,787. Numerous push-in type connectors followed this commercial success. Other patents of later vintage concerned with the push-in type connector and having two side-by-side cam contacts on the same strip of metal include the U.S. Pat. Nos. 3,339,170 and 3,467,941 assigned to the same assignee as this application. Also U.S. Pat. No. 3,489,985 discloses a contiguous cam contact for a convenience outlet which is in its structure quite similar to that disclosed in the subject application.
Other relevant patents are the U.S. Pat. Nos. 2,974,301; 3,001,168; and 3,325,768 which were cited as references in the U.S. Pat. No. 3,489,985 assigned to the same assignee as this application.
One problem which has developed in the employment of the electrical contact of the device taught in the U.S. Pat. No. 3,489,985 is that very close dimensions of the contiguous cams must be maintained in order to prevent or avoid interference of one cam with the other. Such interference is particularly disadventageous where it causes reduction of the gripping power of an adjoining cam on a wire so that less than a full pressure contact, and suitably low resistance, is maintained between the inserted wire and the wire contact. One problem encountered in use of the receptacle of the U.S. Pat. No. 3,489,985 patent with its eight push-in connectors, is that it could be used only with the smaller size wires normally employed in branch circuits in residences. With the introduction of the copper clad aluminum wire the contact itself could function perfectly well with the copper clad wire but the wire diameter required is frequently a No. 10 size wire and this wire cannot be accommodated in the contact push-in connector structure of the U.S. Pat. No. 3,489,985.
Accordingly a problem arose in attempting to maintain the compactness of structure so that the receptacle with eight push-in connectors could be used in home construction, where it has its principal application, and yet accommodate the larger size wires which were an incident of the change to copper clad aluminum conductors in the home building trade.
An effort was made to eliminate this problem by enlarging the two openings seen in the U.S. Pat. No. 3,489,985 to a single overall opening of oval shape so that two No. 10 wires could fit into the opening and make the proper contact with the metal strip within the receptacle. While this permitted larger wire entry and contact was successfully established with the inserted wires, it was found that where a No. 10 copper clad wire was employed in combination with a No. 12 or No. 14 copper or copper clad wire in the same opening and the wires were manipulated as a consequence of the insertion of the receptacle into its wall box where it was to be employed, the contact on the smaller diameter wire was sometimes reduced so that a high resistance contact developed or that the contact with the smaller diameter wires was in fact broken due to the insertion of the wired receptacle into its wall box.